Not Applicable
Not Applicable
1. Field of the Invention
This invention relates to the routing of data packets to and from a mobile node in a visited wireless data network when the mobile node""s home address matches the home address of another mobile node in the same visited network.
2. Description of the Prior Art
In a wireless data network implemented according to a mobile networking standard, such as the Mobile Internet Protocol (IP) specifications (RFC2002) promulgated by the Internet Engineering Task Force (ETF), a mobile node is able to change its point of attachment to a data network, such as the Internet, and communicate with other data network nodes at any location without changing its home (IP) address. While communicating with other network nodes, the mobile node communicates across an air interface to a base station, and typically sends and receives data packets over a Point-to-Point Protocol (PPP) link that connects the mobile node to a centralized network element known as an Interworking Function (IWF) that hides cellular specific aspects from the general IP network. According to the IETF Mobile IP specifications, the IWF is further linked to send packets to or receive packets from a Foreign Agent, which is a router located in the mobile node""s visited network. When sending packets to the Foreign Agent, the IWF removes the PPP header; when receiving packets from the Foreign Agent, the IWF adds the PPP header. The Foreign Agent and a Home Agent (a router located in the mobile node""s home network) exchange data packets between each other via a tunnel. A tunnel is a path followed by the user""s data packet while it is encapsulated in another packet.
Although existing Mobile IP standards can manage data transmissions between mobile nodes that attach to the public Internet, they do not provide specifications for IWF/Foreign Agent handling of communications between mobile nodes that attach to private networks. This limitation is significant because users of wireless data services desire the ability to access their private networks to allow them to perform various tasks such as viewing intranet web pages and reading and dispatching email.
The private network limitation inherent in existing Mobile IP standards specifically relates to the lack of specifications for handling potentially overlapping home addresses of mobile nodes. A private home address may overlap with an identical address from a different private network because, unlike addresses on the public Internet, private addresses are not globally administered through a registration system. Rather, they are selected by private network administrators from the IP address pools reserved for private networks.
Under current Mobile IP standards, the problem with overlapping home addresses arises when two mobile nodes, each associated with a separate private network, are to be served by the same visited wireless network/IWF and the same Foreign Agent. In this case, the Foreign Agent cannot distinguish between two such nodes with identical home addresses when transmitting data packets in the reverse traffic direction (i.e., from the mobile nodes to their corresponding Home Agents). The Foreign Agent is unable to ascertain the difference between the two mobile nodes because it relies on the mobile node""s home address to determine the Home Agent to which the data packets should be sent -or tunneled. When the two mobile nodes have the same home address, the Foreign Agent cannot perform its normal reverse direction routing functions.
In the forward traffic direction (i.e., from the Foreign Agent to the mobile node), a similar problem arises because the IWF does not have enough information to transmit the data packets to the correct mobile nodes. To correctly transmit the data packets, the IWF needs, but lacks, the critical information specifying which Home Agent sent the data packet to the Foreign Agent.
Accordingly, there is a need in a wireless data network for a method and system that support the correct transmission of data packets to and from a roaming mobile node when that node has an IP address that matches the IP address of another mobile node linked to the same visited network. More particularly, a method and system are needed for distinguishing between mobile nodes with overlapping IP addresses during the transmission of data packets to and from an Interworking Function and a Mobile IP Foreign Agent. cl SUMMARY OF THE INVENTION
A system and method in accordance with the invention support the correct routing of data packets to and from mobile nodes that are connected to the same visited data network and have overlapping home (IP) addresses. Preferably through associated storage tables, an IWF and a Foreign Agent in a visited data network retrieve and share a mobile node identifier that can differentiate between mobile nodes with identical home addresses.
In preferred embodiments of the invention, the mobile node identifier that can uniquely identify a mobile node is a Network Address Identifier (NAI) that is stored in a Mobile Identity table associated with the IWF and in a Visitor List table associated with the Foreign Agent. As a data packet travels across the visited data network in the reverse traffic direction, a composite packet is formed from the data packet and the NAI at the IWF and sent to the Foreign Agent. The Foreign Agent extracts the NAI and uses it with the Visitor List table to look up a Home Agent that corresponds to the mobile node. Once the mobile node""s Home Agent is determined, the Foreign Agent sends the data packet to that Home Agent. When a data packet moves in the forward traffic direction, a similar composite packet is formed by the Foreign Agent and sent to the IWF. The IWF extracts the NAI and uses it to find the mobile node""s link identifier in the Mobile Identity table. Once the link identifier is known, the IWF sends the data packet to the correct mobile node.